Might still be worth checking the connection wires to the small LED pcb as well - they're all single core stiff wires soldered direct between the pcbs if I recall, that can be easily damaged if bent or moved too much. I'm wondering if maybe a bad, high resistance, joint on the signal input side might eventually give the sort of symptoms you describe (?).
I've only ever seen all the LED's lit running with dummy loads, and almost full power, but 70% to get just the 1W LED lit seems higher than I remember.
Alan
I've only ever seen all the LED's lit running with dummy loads, and almost full power, but 70% to get just the 1W LED lit seems higher than I remember.
Alan
cheers alan.
i did re flow all of the cable joints, they are realy poor quality cables, not even copper.
i did re cap it all in the end as its not a big job and gives the unit plenty of life going forward.
the amp is working well, so ive tried in all modes, inc the phono, which i have to say is pretty good,very little noise.
im pretty sure its working as it should be TBH so im not going to mess about with this anymore.
ive tidied all the cables up, cleaned all the pots and switches, so no crackling at all
paul
i did re flow all of the cable joints, they are realy poor quality cables, not even copper.
i did re cap it all in the end as its not a big job and gives the unit plenty of life going forward.
the amp is working well, so ive tried in all modes, inc the phono, which i have to say is pretty good,very little noise.
im pretty sure its working as it should be TBH so im not going to mess about with this anymore.
ive tidied all the cables up, cleaned all the pots and switches, so no crackling at all
paul
i noticed with this amp, as with some older units, that there is a bit of a thump when turned on,but this one is quite a tasty thump and moves the drive units quite a bit.
In the past some amps have been known to damage certain tweeters.
this amp does have a coupe of caps across the mains switch(suppression i guess?) and they are ok because i tested them.
any ideas how this thumping can be reduced???
In the past some amps have been known to damage certain tweeters.
this amp does have a coupe of caps across the mains switch(suppression i guess?) and they are ok because i tested them.
any ideas how this thumping can be reduced???
It could be hard to determine if it is a fault or a characteristic. You need to isolate the pre and power sections as a first step.
There was a NAD thread where I even went as far as simulating the mute circuit but I can't find the thread. You would need to be sure yours was the same as well. This one had FET muting in series with the pre/power amp signal feed and it relies on a third momentary contact on the mains switch.
I still have the sim
If it is similar it will look a bit like this.
There was a NAD thread where I even went as far as simulating the mute circuit but I can't find the thread. You would need to be sure yours was the same as well. This one had FET muting in series with the pre/power amp signal feed and it relies on a third momentary contact on the mains switch.
I still have the sim
If it is similar it will look a bit like this.
Attachments
I think this is the thread you're referring to Mooly:
https://www.diyaudio.com/forums/solid-state/319464-dc-offset-nad-3120-preamp-output.html
I think Poundy's 3020 pre-dates the NAD muting circuit though, it was only introduced with the (slightly later iterations I believe).
For completeness - the diode modification of the muting circuit (to reduce pre-out offset) works perfectly, albeit using a silicon diode - I didn't have a germanium to hand. I've been using it for the past year or so.
Alan
https://www.diyaudio.com/forums/solid-state/319464-dc-offset-nad-3120-preamp-output.html
I think Poundy's 3020 pre-dates the NAD muting circuit though, it was only introduced with the (slightly later iterations I believe).
For completeness - the diode modification of the muting circuit (to reduce pre-out offset) works perfectly, albeit using a silicon diode - I didn't have a germanium to hand. I've been using it for the past year or so.
Alan
well done for finding it.
So it sounds like there is some influence (DC shift in level) from the preamp section in making the thump worse.
To investigate this (and it may be normal in the end) would need detailed examination of the full circuit diagram and how the mute in your version operates and what time delays it has.
To investigate this (and it may be normal in the end) would need detailed examination of the full circuit diagram and how the mute in your version operates and what time delays it has.
I perhaps poorly worded my last comment - instead of "pre-dates the NAD muting circuit", I should have said pre-dates the NAD automatic muting circuit.
The original muting was a simple manual pushbutton 'mute' switch on the front of the amp, dropping both of the pre-out signals to ground, via 1k5 resistors.
Alan
The original muting was a simple manual pushbutton 'mute' switch on the front of the amp, dropping both of the pre-out signals to ground, via 1k5 resistors.
Alan
I suspect the 'thump' you referred to is just due to the asymmetric power supplies used in the pre-amp stage, and specifically how they develop during the first second when you turn it on.
I tried modelling the PS in LTSpice, albeit with different transistor & diode models (I'm still learning LTSpice and haven't mastered adding new library components yet), and I think the +ve supply lags noticeably behind the -ve, maybe enough to give you a transient dc offset at the pre-out sockets, that you hear as the 'thump'.
There's no simple way to add the later muting ciruit to your model, but to be honest, fitting a dedicated speaker protection relay & pcb would be a better solution. They usually include start-up / shut-down muting as well.
Alan
I tried modelling the PS in LTSpice, albeit with different transistor & diode models (I'm still learning LTSpice and haven't mastered adding new library components yet), and I think the +ve supply lags noticeably behind the -ve, maybe enough to give you a transient dc offset at the pre-out sockets, that you hear as the 'thump'.
There's no simple way to add the later muting ciruit to your model, but to be honest, fitting a dedicated speaker protection relay & pcb would be a better solution. They usually include start-up / shut-down muting as well.
Alan
I would agree with Alan that the most reliable option would be a speaker relay delay. That should give silent switch on and off.
Without knowing how good or bad the standard design actually is makes it difficult to know if there is a fault or not, at least without some more involved fault finding and elimination of various possibilities.
You would need to power the amp up with the power amp inputs isolated (and perhaps tied to ground depending on the circuit) and then see what the intrinsic thump is like. That would be as good as it gets and nothing in front of that would improve or alter that (other than adding the speaker relay delay).
Without knowing how good or bad the standard design actually is makes it difficult to know if there is a fault or not, at least without some more involved fault finding and elimination of various possibilities.
You would need to power the amp up with the power amp inputs isolated (and perhaps tied to ground depending on the circuit) and then see what the intrinsic thump is like. That would be as good as it gets and nothing in front of that would improve or alter that (other than adding the speaker relay delay).